Add base infrastructure

[ldmi3i]

You need to add base interfaces and project structure to provide the possibility to:

1. Update ApiSpecDoc - check if that model is really new, and if it is - calls update in DB.
2. Add middleware (in the future probably will contain cache) and services to search and get ApiSpecDoc.
3. Add entities and repositories draft.

(probably we'll need some discussion here, but we need some draft to start)